1. Technological Field
The present invention relates to a test apparatus. More particularly, the invention relates to a test apparatus for testing a device-under-test.
2. Background Art
A memory test apparatus applies and writes an address signal and a test signal generated by a pattern generator to a memory-under-test. It then compares the test signal read out of the memory-under-test with an expected value signal generated by the pattern generator corresponding to the test apparatus and stores the comparison result to a failure analysis memory. After that, the memory test apparatus analyzes the comparison result stored in the failure analysis memory to judge if the memory-under-test is failure-free.
With the recent increase of speed of operating frequency of MPU, operating speed of a memory-under-test such as DRAM is also increasing. However, the failure analysis memory used in the conventional memory test apparatus is composed of SRAMs whose improvement in terms of memory capacity is slow as compared to the DRAM. Therefore, the failure analysis memory having the equal operating speed and memory capacity with those of the memory-under-test is realized by composing the failure analysis memory by a plurality of SRAMs so as to operate through interleave operation.
However, the operating speed of the memory-under-test such as DRAM is increasing continuously even now and it requires a very large number of SRAMs in order to realize the equal operating speed with that of the memory-under-test through the interleave operation of the plurality of SRAMs.
For example, if a test of a memory-under-test having 125 MHz of operating frequency has been realized through the interleave operation of four ways by using four SRAMs, 32 SRAMs must be used and interleave operation of 32 ways must be carried out in order to realize a test of a memory-under-test having 1 GHz of operating frequency.
Still more, because a memory capacity of one SRAM is 1/16 to ⅛ of a memory capacity of one DRAM in general, at least 256 SRAMs are necessary in order to realize the test of the memory-under-test having 1 GHz of operating frequency.
Still more, it is a common practice to reduce a testing cost by simultaneously carrying out the tests of a plural number of memory-under-test by the memory test apparatus and simultaneous testing of 128 memories-under-test is being widely carried out. Accordingly, if 256 SRAMs are necessary for testing one memory-under-test, 32,768 SRAMs are necessary to test 128 memories-under-test in the same time. Therefore, there has been a problem that the memory test apparatus becomes a very large and expensive apparatus just by the failure analysis memory and its peripheral circuits.